(from the article `Stonehenge`) ...erected (one of which, the Slaughter Stone, still survives). Just inside the circular bank they also dugand seemingly almost immediately ...Found on http://www.britannica.com/eb/a-z/a/122

The Aubrey holes are a ring of fifty-six (56) Chalk pits at Stonehenge, named after the seventeenth-century antiquarian John Aubrey. They date to the earliest phases of Stonehenge in the late fourth and early third millennium BC. Despite decades of argument and analysis, their purpose is still unknown although an astronomical role has often been s...Found on http://en.wikipedia.org/wiki/Aubrey_holes